This invention relates to color cathode ray picture tubes of the type having a tensed foil shadow mask for color selection, and is particularly concerned with means and method for establishing the mask and the imaging screen at the proper electrical potential.
The area enclosed by the funnel and faceplate of a color cathode ray picture tube is typically established as a field-free region for the excursion of the electron beams that selectively excite the pattern of discrete phosphor targets deposited on the inner surface of the faceplate that comprises the picture imaging screen. In cathode ray tubes having the tensed foil mask, the faceplate and the corresponding picture imaging screen are usually flat. The field-free region is established by charging the inner surfaces of the funnel and the faceplate and adjacent components to a high potential, typically in the range of 20-25 kilovolts. The surfaces so charged include the conductive coating deposited on the inner surface of the funnel, and an electrically conductive film, normally aluminum, disposed on the back of the picture imaging screen over the phosphor deposits. The shadow mask must also be charged to the same high potential. The shadow mask, which in this case is a tensed foil, is precisely mounted in relation to the screen by means described and fully claimed in one of the referent copending applications heretofore listed. The electrically conductive coating on the surface of the funnel receives the high potential from the metallic "anode button" that protrudes through the wall of the funnel, and which in turn is connected to a conductor leading from a high-voltage power supply.
The luminescing material of the viewing screen commonly comprises a layer of one or more phosphors of different color emission deposited on the inner surface of the display faceplate. This phosphor material is usually "aluminized"; that is an electron-pervious film of aluminum is deposited on the phosphors. The film increases the brightness of the display by acting as a mirror to reflect toward the viewer the light produced by the phosphors when activated by the electron beams. The film typically also carries the high-voltage charge to act as an electron-attractive ultor electrode for the display. The thickness of the film, which is very fragile and easily abraded, is typically about 2,000 Angstroms.
In U.S. Pat. No. 3,489,966 to Bradu et al, there is disclosed a cathode ray tube with a stainless steel post-focusing grid sealed between the sealing lands and the faceplate skirt and the funnel. The grid of wires is cut at the outer surface of the envelope, and a conducting layer on the exterior of the envelope coats the envelope zone which comprises the ends of the wires. A layer of sealing and insulative material over the conducting layer is said to provide for air-tightness and high-voltage integrity. The conductive layer also makes contact with a high-voltage connector for energizing the grid wires. In another configuration in which the high-voltage is applied to the screen, the screen receives operating potential through a terminal which penetrates the faceplate skirt; this terminal in turn is connected to the screen by a conductive paint layer.
A post-deflection cathode ray tube is disclosed in U.S. Pat. No. 3,502,942 to Kahn et al. A unitary color selection and focus-electrode assembly comprises a first electrode for color selection, and a second lens element formed as a mesh of electrical conductors. The color selection electrode and focus electrode assembly are insulated from each other, and each has a different potential thereon. The tube has two conductive coatings on the inside of the envelope, one of which is located on the internal surface of the funnel, but stops short of the plane of the electrode assembly. High voltage for beam acceleration is conducted to the coating through an anode button that penetrates the funnel. A flexible electrical conductor interconnects the color selection electrode with the funnel coating. The second coating is located on the inner surface of the faceplate skirt, and a high voltage for post-deflection focusing is conducted to the coating through a second anode button that penetrates the skirt. A separate spring-like connector projects from the PDF electrode to make contact with a second coating.
Barr in U.S. Pat. No. 3,541,373 discloses a cathode ray tube with a bifurcated spring bridging the shadow mask frame and an internal conductive coating. The spring clips onto the rigid frame, or alternately, is welded to the shadow mask. The distal end makes contact with the inner conductive coating on the funnel which is electrically charged to a high potential. The novelty is said to lie in the bifurcation of the distal end, in which each of two independently operating tines has a different vibration frequency. The result is said to be a more shock-resistant connection and the avoidance of electrical interruption. Also, the positive contact is said to make possible the use of a weaker spring with reduced possibility of mechanical erosion of the conductive coating.
In Davis et al--U.S. Pat. No. 3,898,510--there is set forth through-the-seal conductive means for traversing a CRT envelope seam to effect multiple connections therein. An internal spring-like conductive member straddles the seam at the junction of the funnel and the faceplate skirt to electrically connect the funnel internal conductive coating and the conductive coating on the screen. A conductive member extends through the seam to interconnect the conductive member with an external high voltage connector.
In U.S. Pat. No. 4,333,037 to Andre et al, there is disclosed an arrangement to compensate for the mask-to-screen misregister that occurs when the mask is heated by electron bombardment. A thermally sensitive resistant section inside the tube adjacent to the shadow mask produces a voltage difference between the mask and screen which compensates for misregister caused by the displacement of the electron beams from normal landing points as the mask heats up during the operation. The resistant section may comprise either a PTC or NTC type resistor. The resistance elements are in effect in series with the high-voltage path between the electrically charged inner conductive coating of the funnel and the conductive coating on the screen. The heating of the resistors regulates the potential applied to the screen to provide compensatory electrical correction of the beam landing areas.
Marschka in U.S. Pat. No. 4,344,015 describes a screen contact means for a cathode ray tube. An anode button projecting through the funnel is attached to a screen contact assembly that conducts high voltage directly to the screen, while bridging the gap at which the funnel and faceplate are sealed together. A Nichrome foil member is placed beneath the screen contact point of the conductive member to serve as a non-abrading pad. A member attached transversely to the contact assembly provides for screen-pressure contact with the conductive coating on the inner surface of the funnel.
The following U.S. Patents are also noted: 3,404,303; 4,230,965; 4,243,908; 4,333,033; and 4,433,267.